It is generally well known in the passenger transit vehicle art to employ a door drive mechanism which includes a drive screw engaging a drive nut that is attached to a transit vehicle door so that when the drive screw is rotated such drive nut is moved longitudinally along the drive screw in order to open and close the door. In many instances these drives may have alignment problems which can result in detrimental loads being applied between the drive nut and the drive screw in directions perpendicular to such drive screw. This is particularly the case in a passenger transit vehicle which is not built to close dimensional tolerances and which may also undergo flexure due to a load of passengers.
Any misalignment of the system can significantly increase the friction between the drive nut and the drive screw. This increased friction increases the torque needed to turn the drive screw. Misalignment also increases stresses which may cause premature wear of bearings, fatigue, etc. It may also cause binding of the drive nut and drive screw.